I really am not trying to be argumentative, but to be blunt, you just don't know that.
I don't know exactly what the time interval was between his conversion and his death, but it is certainly probable (and highly likely - given the method of his execution) that he lived long enough to have at least one uncharitable thought/statement/action towards his roman executioners.
You have a good idea, as the centurions had to smash his legs to get him to die before the Passover. No one can seriously try to tell me the guy looked down on the soldiers who BROKE HIS LEGS and said some pietistic drivel like "bless you, my son." Nope. Born at night, but not LAST night. Kind of like my wreck on a motorcycle some years back. I went over the handlebars at about 40 mph, hit on my (helmented) head and neck. Felt a loud POP, and a searing pain. My thought was "OK, bud, you have punched your f*cking ticket." I then was reminded of Christ, his death, and my assurance of pardon and the fact that if I were dying, it was a good gig, or at least the pathway into something REALLY good. All these thoughts went thru my mind (including the f word) in a milisecond. Then I hit, I bumped, I scraped, I bounced, I rolled, I broke a new bone it seemed every time I hit the ground again. I remember thinking when my foot snapped "Damn, if I am going to die I wish I would hurry up, this HURTS!" I am going to die just like I live. A sinner filled to the brim with filth if my heart can puke it out, and one who trusts in the mercy and blood of Christ to give me a righteousness that I can never attain for myself. I wish the first part (about the filth) were not true, but it is. I can push it down some, but give me the right set of stresses, enough fear, and enough self pity and it is like I never heard of God. It was true for the thief, and it is true for everyone else on this miserable mud ball we call Earth. People who claim otherwise just kid themselves.